The present invention relates to an integrated magnet body used in a motor for an electric vehicle and a motor for a home electric appliance, and a motor incorporating the same. More specifically, it relates to an integrated magnet body excellent in insulating property and effective volume ratio, and a high efficiency motor incorporating the same.
As a motor for an electric vehicle (such as EV: electric vehicle and HEV: hybrid electric vehicle) and a motor for a home electric appliance, for example, brushless motors, such as so-called IPM (interior permanent magnet motor) and SPM (surface permanent magnet motor), have been developed, which uses a rare earth metal-based permanent magnet represented by an Rxe2x80x94Fexe2x80x94B based permanent magnet embedded in a rotor formed with silicon steel plates or the like.
In recent years, improvements in materials for rare earth metal-based permanent magnet proceed, and performances of motors are also improved according thereto. However, because the rare earth metal-based permanent magnet has electroconductivity, it has problems where such disadvantages are caused upon application of an alternating current magnetic field on the magnet, in that an eddy current is generated in the magnet to lower the efficiency of the motor as an eddy current loss, the characteristics of the motor are deteriorated by heat demagnetization of the magnet.
As a method for lowering the eddy current occurring in the magnet, there is such a method in that the magnet is divided, and plural magnet pieces are laminated with electric insulation therebetween to form an integrated magnet body (see, for example, JP-A-4-79741). Conventionally, upon employing the method, for example, an adhesive having insulating property is coated on the magnet pieces, and one of the magnet pieces is adhered and fixed with another.
However, in the method where an adhesive having insulating property is coated on the surface of the magnet pieces, followed by adhering and fixing, it is necessary that the film thickness of the adhesive formed between the magnetic piece and another magnetic piece is as thick as 100 xcexcm or more to assure the prescribed adhesion strength. Therefore, in an integrated magnet body having the prescribed dimension, even when sufficient insulating property can be obtained among the respective magnet pieces, the volume ratio of the magnet pieces themselves constituting the integrated magnet body (hereinafter referred to as an effective volume ratio) is lowered corresponding to the thickness of the adhesive. As a result, the effective magnetic flux density is lowered to cause deterioration of the characteristics of the motor, which brings about deterioration of the efficiency of the motor. Furthermore, in this method, the thickness of the adhesive influences the dimensional accuracy, and thus an integrated magnet body having high dimensional accuracy cannot be obtained.
Accordingly, an object of the invention is to provide an integrated magnet body excellent in insulating property and effective volume ratio, and a high efficiency motor having the same installed therein.
As a result of various investigations made by the inventors in view of the foregoing standpoints, it has been found that a film having excellent insulating property only with a thin film is formed between one magnet piece and another magnet piece, and the film thickness of the insulating film and the ratio of the total sum of the thickness of the insulating films to the overall length in the laminating direction of the integrated magnet body are set at particular values, whereby an integrated magnet body excellent in insulating property and effective volume ratio can be obtained, and an efficiency of a motor can be improved by installing the integrated magnet body in the motor.
The invention has been made based on the foregoing findings, and the integrated magnet body of the invention is, as described in the claim 1, an integrated magnet body formed by laminating and securing a plurality of pieces of magnet through an insulating film between pieces of magnet, characterized in that the insulating film has a film thickness of 0.01 xcexcm or more, and a ratio (l/L) of a total sum of the thickness of the insulating films (l) to an overall length in the laminating direction of the integrated magnet body (L) is in a range of from 0.0005 to 3%.
The integrated magnet body as described in the claim 2 is an integrated magnet body as described in the claim 1, characterized in that the film thickness of the insulating film is 50 xcexcm or less.
The integrated magnet body as described in the claim 3 is an integrated magnet body as described in the claim 1 or 2, characterized in that the ratio (l/L) of the total sum of the thickness of the insulating films (l) to the overall length in the laminating direction of the integrated magnet body (L) is in a range of from 0.01 to 1%.
The integrated magnet body as described in the claim 4 is an integrated magnet body as described in one of the claims 1 to 3, characterized in that the insulating film is an inorganic insulating film containing, as a main component, at least one selected from a chromium oxide, a phosphorous oxide, a silicon oxide, an aluminum oxide, a titanium oxide and a zirconium oxide.
The integrated magnet body as described in the claim 5 is an integrated magnet body as described in one of the claims 1 to 3, characterized in that the insulating film is an organic insulating film containing a thermoplastic resin and/or a thermosetting resin.
The integrated magnet body as described in the claim 6 is an integrated magnet body as described in one of the claims 1 to 5, characterized in that the integrated magnet body is formed by securing by encompassing and integrating, with an organic resin, a laminated body obtained by laminating a plurality of pieces of magnet through an insulating film between the pieces of magnet.
The integrated magnet body as described in the claim 7 is an integrated magnet body as described in one of the claims 1 to 5, characterized in that the integrated magnet body is formed by securing by binding, with a high strength fiber strip, a laminated body obtained by laminating a plurality of pieces of magnet through an insulating film between the pieces of magnet.
The integrated magnet body as described in the claim 8 is an integrated magnet body as described in one of the claims 1 to 7, characterized in that the pieces of magnet are a rare earth metal-based permanent magnet.
The motor of the invention is, as described in the claim 9, characterized by comprising an integrated magnet body as described in one of the claims 1 to 8 installed therein.